<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>

<body>
  <script>
    function foo() {
      var a = 10;

      function fn1() {
        console.log(a);
      }

      function fn2() {
        var b = 10;
        console.log(b);
      }
      fn2();
    }
    foo();
  </script>
</body>

</html>